PROJECT SUMMARY The prevalence of cannabis use has increased significantly in recent years among US adults aged ? 50 years. With increased availability and use of cannabis by older adults, a rigorous evaluation of the benefits and risks of cannabis use in these individuals is necessary. Aging is characterized by physiological and social changes that make older adults vulnerable to chronic disease and geriatric conditions including cognitive impairment and falls3. Unintentional falls are a common event for older adults and a major cause of morbidity and mortality linked with a decline in functional status and disability. Moreover, falls and cognitive impairment are a ?well- known couple?; as older adults with moderate to severe cognitive impairment have a higher risk of falls, with an annual incidence of around 60?80%, which is twice the rate of cognitively normal older adults. Impaired cognitive function is an effect of cannabis use, and there is increasing evidence that those effects may persist later in life. Therefore, the physiological effects of chronic cannabis use may further increase falls in older adults via alterations in gait and cognition. Studies have shown reduced neural activity in the frontal brain networks and associations with increased fear of falling in older adults. It is also known that in regular cannabis users, the effects of cannabis may have an impact on cognitive-motor skills and brain mechanisms that modulate coordinated movement. The goal of this application is to investigate the neural correlates of fall risk and cognitive and motor function in individuals who initiate drug use after the age of 50. We will use FDG-PET to determine brain activity. Fall risk and cognitive/motor function will be assessed with the measures from the NIH Toolbox and a fall risk model. Our central hypothesis is that older chronic cannabis users are at a higher fall risk than older non-users, which is associated with reduced cerebral FDG uptake. This work will lay the foundation for larger grants (R01) investigating the influence of the compound action of different cannabinoids. These results are expected to provide critical and timely data to the public and health professionals regarding the effects of self-directed cannabis use on increased fall risk and if clinicians need to access cannabis use when determining fall risk and deciding prevention strategies.